1. Field of the Invention
This invention relates generally to power supplies and, more specifically, the present invention relates to a switched mode power supply.
2. Background Information
All electronic devices use power to operate. A form of power supply that is highly efficient and at the same time provides acceptable output regulation to supply power to electronic devices or other loads is the switched-mode power supply. In many electronic device applications, especially the low power off-line adapter/charger market, during the normal operating load range of the power supply an approximately constant output voltage is required below an output current threshold. The current output is generally regulated below an output voltage in this region of approximately constant output voltage, hereafter referred to as the output voltage threshold.
In known switched mode power supplies without secondary current sensing circuitry, minimizing the variation of the output current at the output voltage threshold is performed with complex control schemes. Typically, these schemes include the measurement of input voltage, output diode conduction time and peak primary current limit. Some or all of this measured information is then used to control the regulator in order to reduce the variation of the output current at the output voltage threshold.